Short gap electric arc heater with opposing gas swirl

ABSTRACT

An electric arc heater useful in chemical processing operation where a thin annular disc is placed between two axially disposed hollow electrodes. The disc aids in channeling a gas which may be tangentially introduced into a chamber within the electrodes where chemical processing occurs. The gas flows on either side of the disc and between the electrodes to blow electrical arclets which are struck between one electrode and the disc and between the disc and another electrode into the arc chamber, stretching the arclets transversely with respect to the axis of the arc chamber. The arclets join to form a single arc once the arclets have been blown a sufficient distance away from the electrically conducting disc. The opposing introduction of gas on either side of the disc into the arc chamber reduces net swirling and reduces centrifugal forces within the gas which otherwise may create boundary layers of cool heavy gas against the side wall of the arc chamber which would in turn cause poor temperature distribution transversely across the arc chamber and impede heat removal through the walls of the arc chamber or throw heavy process particles into the gap thus creating a potential for unwanted short circuits between electrodes.

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United States Patent [1 1 Wolf et al.

[111 3,760,145 Sept. 18, 1973 Inventors: Charles B. Wolf, Irwin; Maurice G.

Fey, Turtle Creek, both of Pa.

[73] Assignee: Panelera International Inc., Salt Lake City, Utah [22] Filed: Dec. 13, 1971 [21] Appl. No.: 207,453

[52] US. Cl. 219/121 P, 313/231 [51] Int. Cl. 823k 9/00 [58] Field of Search 219/121 R, 121 P, 219/74, 75; 313/231; 13/9 [56] References Cited UNITED STATES PATENTS 3,521,106 7/1970 Hess"; 219/121 R X 3,522,015 7/1970 Ganiero et al. 219/121 R X 3,329,865 7/1967 Jaatinen 219/121 P X 3,343,019 9/1967 Wolf et a1, 219/75 X 3,309,550 3/1967 Wolf et a1 219/121 P X 3,474,279 10/1969 Kereny et a1... 219/121 R X 3,360,988 1/1968 Stine et al. 219/121 P X 3,360,682 12/1967 Moore 219/121 P X Primary Examiner-.1. V. Truhe Assistant Examiner-Gale R. Peterson Attorney-A. T. Stratton et al.

[57] ABSTRACT An electric arc heater useful in chemical processing operation where a thin annular disc is placed between two axially disposed hollow electrodes. The disc aids in channeling a gas which may be tangentially introduced into a chamber within the electrodes where chemical processing occurs. The gas flows on either side of the disc and between the electrodes to blow electrical arclets which are struck between one electrode and the disc and between the disc and another electrode into the arc chamber, stretching the arclets transversely with respect to the axis of the arc chamber. The arclets join to form a single are once the arclets have been blown a sufficient distance away from the electrically conducting disc. The opposing introduction of gas on either side of the disc into the arc chamber reduces net swirling and reduces centrifugal forces within the gas which otherwise may create boundary layers of cool heavy gas against the side wall of the arc chamber which would in turn cause poor temperature distribution transversely across the arc chamber and impede heat removal through the walls of the arc chamber or throw heavy process particles into the gap thus creating a potential for unwanted short circuits between electrodes.

g 8 Claims, 7 Drawing Figures SHORT GAP ELECTRIC ARC HEATER WITH OPPOSING GAS SWIRL CROSS-REFERENCE TO RELATED APPLICATION Apparatus and method of increasing arc voltage and gas enthalpy in a self-stabilizing arc heater by Maurice G. Fey, Ser. No. 15,597, filed Mar. 2, 1970, now Pat. No. 3,663,792.

BACKGROUND OF THE INVENTION This invention relates to are heater apparatus in general and in particular it relates to are heater apparatus employing the introduction of process gas tangentially through a narrow gap between electrodes into an arc chamber.

The introduction of the gas tangentially into the narrow gap acts to force an electric arc which has been struck between the electrodes into the arc chamber where the arc is elongated, increasing the arc voltage and power factor thereof, and where the arc may then heat the gas for chemical processing. An arc heater of this general type is shown and described in US. Pat. No. 3,343,019 issued to C. B. Wolf et al., Sept. 19, 1967, entitled High Temperature Gas Arcing Heater with Liquid Cooled Electrodes and Liquid Cooled Chamber Walls. The introduction of gas through a narrow gapbetween electrodes of opposite polarity and differing voltages to blow an electric arc which has been struck between the two electrodes into the chamber for chemical processing is known in the art. It is also known to introduce the gas tangentially through a manifold ring so that less gas may be forced into the chamber per unit time but that the arc may be blown speedily and with sufficient force tangentially into the chamber for the purpose of quickly establishing a high voltage are in the chamber. It is known that gas swirl occurs when the gas is introduced tangentially and that in some instances the swirl may be beneficial. It is also known, however, the swirling gas may have a disadvantage in some instances in that it may cause centrifugal forces which tend to force the colder, heavier particles of gas outward against the inner walls of the arc chamber leaving the lighter hotter particles near the middle or axis of the arc chamber where they are further heated. This results in relatively discrete layers of cold and hot gases where the complete mixing of the products to be chemically combined in the process chamber take place in a narrowed volume of the arc chamber. It would be advantageous to be able to introduce gas tangentially through the narrow gap between electrodes into the arc heating chamber without generating a vortex or swirl. In another instance, when gas is tangentially forced into an arc heating chamber, in which a magnetic field is employed to assist in moving the arc roots which reside on each electrode and in which the arc is propagated or maintained by an alternating current backup voltage or backup source, during one-half cycle of alternating current the force of gas flow and the arc root motion are additive, that is the magnetic field and the gas both tend to move the arc in the same direction. However, when the magnetic field is in opposition to the flow of the gas the arc is caused to reside for a. relatively longer period of time in one spot thus possibly, burning or eroding portions of the electrode. It would be advantageous to cause the electric arc generating means and the electromagnetic means to cooperate with the flow of the gas such that any are root which corresponds to current leaving an electrode is always caused to move rapidly so that erosion may be minimized.

SUMMARY OF THE INVENTION In accordance with the invention, a thin annular disc of electrically conductive material is disposed between two axially aligned electrodes of an electric arc heater apparatus. An electric are which is subsequently used to heat gases and other materials in an arc chamber within the arc heating apparatus is periodically struck in sections between one electrode and the electrically conducting disc or ring and the electrically conducting disc or ring to the other electrode. Whereupon relatively cool process gas, which may be electrically insulating when cool, flowing through the highly restrictive regions between the electrodes and the disc forces the arclets into the chamber. Manifold rings are provided on either side of an insulating member which supports the previously described conducting disc or ring. Gas is provided between an electrode and the disc into the arc chamber tangentially and transversely to the axis of the electrodes. This is done on either side of the electrically conducting ring but in opposite tangential directions in each case so that the effect of swirling within the arc chamber as the gas enters the arc chamber is reduced or cancelled. This has the beneficial effect of reducing centrifugal forces on the heaver particles of gas. Thus heavier and lighter particles are not separated as in a centrifuge where a region of relatively cool gas and a distinguishable region of relatively hot gas is created. Consequently, the portion of the gas in which chemical combination takes place is not restricted.

In addition, since the volumetric flow of gas is restricted by the placement or disposition of the disc within the narrow gap, less gas is supplied per unit of time to the arc chamber however, the velocity of the gas is increased thus blowing the arclets more quickly into the arc chamber where they may join to form a single arc once they have cleared the disc between the electrodes.

Since tangential components of force are produced in opposite directions beside either electrode, the cooperation of the are producing electrical power source and the electromagnetic electrical power source may be so phased that that portion of the arc current which is leaving an electrode at any particular instant of time may be forced to move quickly on the electrode due to the cooperating effect of the tangential component of force of the gas and the magnetic field acting on the arc current. Consequently, that portion of the arc root which represents electrons leaving the surface of one of the electrically conducting electrodes is always moved faster than that portion of the arc root which represents or comprises electrons entering the other electrode.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference may be had to the preferred embodiment exemplary of the invention shown in the accompanying drawings in which:

FIG. I shows a cutaway side elevation of a portion of an arc heating apparatus including electrode portions, are heating chamber, electromagnet and an electrically conducting disc;

FIG. 2 shows a view of a gas manifold where the manifold has radial gas inlets;

FIG. 3 shows a view of a gas manifold where the gas inlets are generally tangentially oriented with respect to the radius of the manifold;

FIG. 4 shows a magnified view of the protruding electrically conducting disc in the gap of the arc heater shown in FIG. I when an arc is initially struck;

FIG. 5 shows a view of the protruding electrically conducting disc of FIG. 4 at some time after the arc is struck;

FIG. 6 shows the effect of electromagnetic and fluid additive forces on an arc root; and

FIG. 7 shows a view similar to FIG. 6 but with the current of the arc flowing in the opposite direction from that shown in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and in FIG. 1 in particular, a view of a portion of an arc heater apparatus such as disclosed and claimed in copending application, entitled Apparatus and Method of Increasing Arc Voltage and Gas Enthalpy in a Self-Stabilizing Arc Heater, Ser. No. 15,597, filed Mar. 2, 1970, now US. Pat. No. 3,663,792 by Maurice G. Fey and assigned to the assignee of the present application is shown.

The operating characteristics of the disclosed invention are described in greater detail in the previously mentioned application. However, for the general purposes of a brief description, it may be said that a portion of the arc heater apparatus 10 comprises an arc chamber 20 formed by electrodes 22 and 24 having curved portions 26 and 27, respectively. In the present application, a ring or disc of electrically conducting material 28 such as but not limited to an alloy of copper is added and affixed to a modified insulating barrier or spacer 26 adapted to receive the disc 28.

Adjacent the curved portions 26 and 27 of electrodes 22 and 24, respectively, are gas manifold headers or sections 32 and 30 respectively. Gas ports for the entrance of a fluid such as a gas are shown at 36 and 38, respectively. The fluid enters the vicinity of manifold rings 32 and 30 at openings or orifices 40 and 42, respectively. The gas is channeled through slots 44 and 46 of rings 32 and 30, respectively, to the region of the annular gap 34, in which the electrically conducting protrusion or disc 28 resides. Also shown are electromagnets 50 and 56, either or both of which may be omitted under certain circumstances, disposed near electrodes 24 and 22,'respectively, and having electrically conducting leads for energizing purposes. As an example, electromagnet 50 may have electrically conducting input and output lines 52 and 54 and electromagnet 56 may have input and output energizing lines 58 and 60. Also provided are securing means 62 and 64 whereby structural members 63 may be joined or secured together to provide support for the previously mentioned elements or parts of the arc heater apparatus. A source of electrical power or potential 68 which may be either of the alternating current or direct current type is connected to either electrode 22 or 24 so that a completed circuit through are 72 may be formed.

Where the source of power 68 is an alternating current source of power, a choke or ballast 70 may be included in the circuit for arc current control. Are 72 is shown in a partially blown or elongated form or condition. It is to be understood that are 72 is initiated in the narrow regions between electrodes 22 and 24 otherwise known as gap 34 generally parallel to the axis (not shown) of the electrodes 22 and 24 and near the protrusion 28.

A novel construction feature in the present application, in addition to the electrically conducting ring 28, is the plurality of oppositely directed cuts or grooves in FIG. 1 is disposed to cause a cancelling effect of the gas swirl in the vicinity of the curved surfaces 26 and 27 of electrodes 22 and 24, respectively, thus eliminating or reducing gas swirling in arc chamber 20. The gas which enters ports 40 and 42 from external ports 36 and 38, respectively, is channeled tangentially in opposite directions through channels, grooves, slots, or openings 44 and 46 into the vicinity of gap 34 where each component of gas from the respective manifold rings 32 and 30 squeezes or forcefully slides between electrode 22 and electrically conducting ring 28 in one instance and electrode 24 and electrically conducting ring 28 in the other instance, at opposites or substantially opposite angles from the radius of the electrode. Although the angles need not be exactly opposite they should have components of magnitude in the opposite direction for the aforementioned cancelling efi'ect. Said in another way, the gas flowing in that portion of gap 34 between the electrically conducting ring 28 and electrode 24 may have a component of direction generally out of the page upon which FIG. 1 is drawn and the gas flowing into chamber 20 between electrically conducting ring 28 and electrode 22 may have a component of direction into the page upon which FIG. 1 is drawn. It is not required that the direction of motion with respect to manifolds 30 and 32 be oriented exactly as has been deflowing through groove, cut or slot 44 may have a component of direction flowing out of the same page.

As stated, the gas not only flows radially into the arc chamber 20 but has components in opposite directions or into and out of the page upon which FIG. 1 is drawn.

ented slots, grooves, or cuts 46A so that the gas which may flow into the arc chamber flows substantially radially into the arc chamber. It has been found that such an introduction of gas into the arc chamber presents a serious problem in that the gas enthalpy or ratio of heat applied by the arc to the mass flow per unit time of gas is relatively low and therefore a manifold ring such as 30A provides for inefficient operation or low enthalpy chemical processing.

A more efficient operation is provided by a manifold ring 308, as shown in FIG. 3, and similar to one disclosed in copending application, Apparatus and Method of Increasing Arc Voltage and Gas Enthalpy in a Self-Stabilizing Arc Heater, Ser. No. 15,597, filed by M. G. Fey on Mar. 2, 1970. With this manifold ring the mass flow rate is reduced by applying gas tangentially through the slots 468 in the ring 30B. The high velocity of the tangentially applied gas sufficiently stretches the are or forces the are or elongates it to create high are voltage and high operating temperatures and yet provides a sufficiently low amount of radial mass flow rate to the gas to allow high values of enthalpy to be imparted to the gas.

Referring now to FIG. 4, an improved version of a gas entry means for an electric arc heater is shown. It will be noted that FIG. 4 represents a magnified portion of FIG. 1 in the vicinity of the narrow gap 34. In this instance, the electrically conducting protrusion 28 is shown disposed generally between two electrodes 22 and 24 having curved surfaces 26 and 27. The gap 34 is shown being broken into a left gap portion 34CL and a right gap portion 34CR. Gas is introduced as shown by arrows 86 and 84. It will be remembered for example that the gas indicated by the arrow 84 may have a direction of tangential velocity out of the page upon which FIG. 4 is drawn and correspondingly the gas shown by arrow 86 may have a component of velocity into the page upon which FIG. 4 is drawn. An arclet 72CL is initially struck between electrode 22 and electrically conduction portion 28, with cold gas as indicated by arrow 86 acting as an insulating medium, and annular arclet 72CR struck between the surface of electrode 24 and electrically conducting protrusion 28. It will be noted that the electrically conducting protrusion or thin annular disc 28 has a portion 82, which is adapted to be fitted onto insulating support means 26C with the aid of a compressive disc or joining or retaining member 80. Portions of the manifold rings 32 and 30 are shown also.

Referring now to FIG. 5, a view similar to that shown in FIG. 4 but at some time later after the arc has been struck and forced to move towards the center of the chamber by the gas flow represented by arrows 84 and 86 is shown. It will be noted that the components of gas flow, as indicated by arrows 86 and 84, tend to force the are 72 into chamber 20 and it will also be noted that the series arclets no longer exist separately as they have been combined to form a single are 72 either by joining or by flashover of one existing arclet to the other electrode or viceversa.

The cool insulating gas provides a higher flashover voltage value between the electrodes 22 and 24 and the protrusion 28, respectively, thus providing for a more efficient electrical operating characteristic of the arc heater. That is, a higher average value of arc voltage to mass flow of gas per unit time may be obtained by using the construction features shown in the FIGS. 4 and 5.

Referring now to FIG. 6, a portion of electrodes 22 and 24 are shown supporting an extended electric arc 72 in arc chamber 20. It will be noted that there is a component of gas swirl 87 due to the tangential introduction of gas into gap 34 as, for example, indicated by arrow 86. Similarly, there is a tangential component of gas flow due to the tangential introduction of gas 84 through the gap 34 and into the chamber 20. Note that the swirls are in opposite directions and that away from gap 34 in an axial direction the tangential component of swirl 87 tends to cancel the tangential component of swirl 85 although the are 72 is caused to be stretched or blown in appropriate fashion at the gap where the cancelling effect of the swirl is not prevalent. Arc 72 is shown having a direction of electrical current flow I which is at generally right angles to a magnetic field line H, which may be produced by electromagnet 50. Near arc root 92, as explained by the Lorentz effect or rule, sometimes known as the Right-hand Rule of Electromagnetics," a component of velocity or are root movement V is applied to the arc root 92 causing the arc root to move in the direction of the arrow including V, which is in additive correspondence with the blow ing effect of swirl gas component 85, also moving in the direction of V, at root 92 so that arc root 92 moves relatively rapidly in the direction of V It will be noted that are root 87 will move relatively less rapidly because its component of movement U due to the interaction of electrical current I, and magnetic field line H, in the vicinity of arc root 90 is in a direction opposite to the direction shown due to gas flow component 87.

The damage which may be done by are propagating between two electrodes such as 24 and 22 is most prevalent in this example at root 92, which may be called a cathode, where the electrical current I, is flowing away from electrode 24 and eroding or taking minute particulate matter away from the electrode 24. Fortunately, if the arc root 92 is moved very rapidly, its tendency to remove material or to scar the electrode surface is statistically lessened. The synchronization or phasing of the electromagnetic field which controls the direction of field lines H and H and the backup voltage source which controls the direction of current I, are cooperative.

Referring now to FIG. 7, as are 72 is restruck the current flow, as indicated by I may be reversed. This makes electrode 22 the cathode. If field lines H and H remain the same and gas swirl paths 87 and 85 remain the same, the component of direction V and U will be reverse from components V and U The velocity V of arc root 90 will then be in an additive relationship to the flowing effect of swirl component 87 such that are root 90 may move more rapidly than are root 92 but in a different direction and acomplish the same purpose discussed with respect to FIG. 6. This time, however, the cathode being electrode 22.

Referring again to FIG. 1, a downstream portion of the arc chamber 20, in which other matter such as particulate matter may be injected into the hot gaseous medium, although not shown, may be relatively free of turbulence and vortex because of the cancelling effect of the oppositely directed tangential components of gas in the vicinity of gap 34. Since the swirling effect is reduced, the centrifugal force tending to cause the colder heavier particles to cluster against the inside of the electrodes and form a heat barrier which constricts the volume of heating the gas to a narrow core within the are chamber is also reduced. A more uniform heat distribution pattern is present over the entire diameter of the arc chamber 20 allowing for a more effective mixture of the matter introduced in portions of the arc heater at a distance removed from the gap 34.

It is to be understood that the novel embodiments may be used in any type of arc heater using either alternating or direct sources of current for arc generation and electromagnetic generation and may be used with multiple or single electromagnetic means. It is also to be understood that the gas or fluid which is introduced into the system through the gap 34 may not be the gas which is reacted upon by the heat generated by are 72. It is also to be understood that the exact angles of tangential introduction of the gas having opposite radial or tangential components may not be exactly complementary or the same.

The present invention has many advantages over the prior art. First, because of the cancelling effect of the swirl there is a better mixing of all gases, both hot and cold, downstream from the gap. In addition, the arc heating apparatus with tangential flow has the capabiL ity of operating at lower flow rates of gas than with straight-through gas injection. The lower gas flow capability allows for the attainment of higher maximum gas enthalpy, and thus provides for more efiicient use of the gas or fluid that is introduced into the system. Another advantage is the fact that there is reduced electrode wear. Also, the alternating arc voltage may rise slowly after an alternating current zero indicating that the arc remains short in length and moves slowly until the Lorentz force overcomes the aerodynamic force whereupon normal arc rotation occurs. It is apparent that an electrode wears least where the aerodynamic force acting on the arc reinforces the Lorentz force. Another advantage is that the effective length of the are in the chamber may be reduced. With the unidirectional swirl arc heater apparatus as described in the prior art an arc root eventually was extended to a position far downstream from electrode gap. This meant that the downstream electrode should be extended axially for prolonged operation at high gas flow conditions. But in an opposed swirl arc heater, this is not the case, the are always attaches itself to the electrode at a point a little more than 12 inches from the gap. Consequently, there is little or no reduction in arc voltage, and the effective length-to-diameter ratio of the electrode is reduced and initial electrode costs reduced. Reduction in electrode length also increases efiiciency as the heat loss to the electrode wall is generally proportional to the wall area. In addition, for safety purposes, dangerous arc attachments to downstream portions are eliminated. Also, there is improved gas mixing because cold gas is not forced away from hot gas centrifugally. Another advantage lies in the fact that solid feedstock particles will not be forced into the gap 34 by centrifugal force.

We claim as our invention:

1. An electric arc furnace apparatus comprising:

a pair of generally tubular, generally cylindrical electrodes, axially spaced to provide a gap therebetween, said gap being generally relatively significantly smaller at its narrowest axial dimension than the axial dimensions of said electrodes;

a source of power for producing an are;

a chamber means, a portion of which includes a portion of said electrodes; and

a means for peripherally providing fluid matter to said gap, said means providing said fluid matter to said gap in different directions to thereby provide a generally net cancelling of the swirling of said fluid at a radially distant portion of said chamber from said electrodes, at least one portion of said means being electrically conducting and extending into the narrowest portion of said gap but being spaced from said electrodes, said electrically conducting portion and at least one of said electrodes generally having an electric arc struck therebetween periodically during operation of said electric arc fumace', said are having arc roots residing on said electrode and said electrically conducting portion of said means, said fluid causing at least one said residing arc root to move to lengthen said are and generally concurrently therewith to cause a portion of said are to be moved into said chamber means further lengthening said arc.

2. The combination claimed in claim 1, wherein said electrically conducting portion of said fluid providing means comprises an electrically conducting disc generally disposed between said electrodes, said arc being provided between said electrodes in two arc portions, one arc portion having a root on a first of said pair of electrodes and another root on said disc, and another arc portion having a root on said disc and another root on a second of said pair of electrodes.

3. The combination as claimed in claim 1 wherein said arc roots reside on said electrodes after said portion of said are is moved into said chamber by said fluid.

4. The combination as claimed in claim 2 wherein said fluid comprises a gas and said arc roots reside on said electrodes after said portion of said are is moved into said chamber by said gas.

5. The combination as claimed in claim 1 including at least one magnetic field producing means wherein said are roots may be additionally moved on said electrodes by the interaction of electrical arc current with said magnetic field.

6. The combination as claimed in claim 4 including at least one magnetic field producing means wherein said arc roots may be additionally moved on said electrodes by the interaction of arc electrical current with said magnetic field.

7. The combination as claimed in claim 6 wherein said magnetic field producing means comprises a source of power and a solenoid coil which cooperate to produce said magnetic field.

8. The combination as claimed in claim 7 wherein said source of power for said magnetic field producing means comprises a first alternating current source of power, said source of power for producing said are comprises a second alternating current source of power, both said sources of power being so phased with respect to each other that when said are begins to propagate from one said electrode at an arc root, that are root is moved by the additive forces from said gas and said magnetic field producing means.

il l 1! I t 5 I UNITED STATES PATENT. OFFICE CERTIFICATE OF CORRECTION Patent m 3,7, ,1"5 Dated September .18, 1973 Inventor) harles B. Wolf and Maurice G. Fey

7 It is certified that etror appears in the above-identified patent andxhat saidLettera Patent are hereby corrected as shown below:

I Column 1,- lines 5 and 6, cancel "[73] Assigneer Panelera International Inc., Salt Lake City, Utah and substitute [73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pennsylvania Signed and sealed this 2nd day of July 1974,

(SEAL) Attest:

EDWARD M. FLE TCI -IERJR. C.MARSHALL DANN Attesting Officer C Commissioner of Patents 

1. An electric arc furnace apparatus comprising: a pair of generally tubular, generally cylindrical electrodes, axially spaced to provide a gap therebetween, said gap being generally relatively significantly smaller at its narrowest axial dimension than the axial dimensions of said electrodes; a source of power for producing an arc; a chamber means, a portion of which includes a portion of said electrodes; and a means for peripherally providing fluid matter to said gap, said means providing said fluid matter to said gap in different directions to thereby provide a generally net cancelling of the swirling of said fluid at a radially distant portion of said chamber from said electrodes, at least one portion of said means being electrically conducting and extending into the narrowest portion of said gap but being spaced from said electrodes, said electrically conducting portion and at least one of said electrodes generally having an electric arc struck therebetween periodically during operation of said electric arc furnace, said arc having arc roots residing on said electrode and said electrically conducting portion of said means, said fluid causing at least one said residing arc root to move to lengthen said arc and generally concurrently therewith to cause a portion of said arc to be moved into said chamber means further lengthening said arc.
 2. The combination claimed in claim 1, wherein said electrically conducting portion of said fluid providing means comprises an electrically conducting disc generally disposed between said electrodes, said arc being provided between said electrodes in two arc portions, one arc portion having a root on a first of said pair of electrodes and another root on said disc, and another arc portion having a rooT on said disc and another root on a second of said pair of electrodes.
 3. The combination as claimed in claim 1 wherein said arc roots reside on said electrodes after said portion of said arc is moved into said chamber by said fluid.
 4. The combination as claimed in claim 2 wherein said fluid comprises a gas and said arc roots reside on said electrodes after said portion of said arc is moved into said chamber by said gas.
 5. The combination as claimed in claim 1 including at least one magnetic field producing means wherein said arc roots may be additionally moved on said electrodes by the interaction of electrical arc current with said magnetic field.
 6. The combination as claimed in claim 4 including at least one magnetic field producing means wherein said arc roots may be additionally moved on said electrodes by the interaction of arc electrical current with said magnetic field.
 7. The combination as claimed in claim 6 wherein said magnetic field producing means comprises a source of power and a solenoid coil which cooperate to produce said magnetic field.
 8. The combination as claimed in claim 7 wherein said source of power for said magnetic field producing means comprises a first alternating current source of power, said source of power for producing said arc comprises a second alternating current source of power, both said sources of power being so phased with respect to each other that when said arc begins to propagate from one said electrode at an arc root, that arc root is moved by the additive forces from said gas and said magnetic field producing means. 